<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script>
var XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";

function boom()
{
  var listbox = document.createElementNS(XUL_NS, 'listbox');
  document.body.appendChild(listbox);
  var listitem = document.createElementNS(XUL_NS, 'listitem');
  listbox.appendChild(listitem);
}
</script>
</head>
<body onload="boom();">
</body>
</html>